Radical polymerisation of ethylenically unsaturated compounds is widely used to harden dental materials such as dental filling materials. In light-curable dental materials, the ethylenically unsaturated compounds are activated to be polymerisable by the application of light, since this allows a “command cure”. By this means the ethylenically unsaturated substances remain workable for an indefinite time, but can be cured at will in a short time by the application of light. Generally the actinic light has a wavelength between about 200 nm and 700 nm, and more often between about 300 nm and 600 nm. In light-curable dental compositions, camphor quinone which allows photopolymerization with visible light is almost exclusively used in combination with an amine as a reductant (co-initiator).
In many cases, it is necessary or convenient to apply the activated dental material or to model it under ambient light. Very often a relatively strong ambient light is needed so that the modelling or application can be carried out with the necessary precision, which leads to several conflicts. If sufficient ambient light is present for accurate and precise use of the dental material, the life time of the activated material is reduced, and the time available for the modelling or application is also reduced. If less ambient light is present, the life time of the material and the time available to model it (“working time”) is increased, but the precision of the modelling is reduced. The lifetime of the material towards ambient light may be increased by, for instance, reduction in the concentration of initiators, or increasing the amount of polymerisation inhibitor present. However both of these measures can lead to a decrease in the physical properties of the light-cured dental material.
It is therefore an object of the invention to provide a light-curable dental material having a sufficient working time under ambient light without compromising the physical properties of the cured dental material. It is another object of the invention to provide a further inhibitor for light-curable dental materials.